Michigan Beogram 8002 Electronic Restoration

The electronic restoration process for the Beogram 8002 mainly involves the two circuit boards, PCB 1 - PCB 2, the Beogram transformer module and the control button panel.

Here are PCB 1 and PCB 2.

Starting with PCB 1, here is a survey of the capacitors that will be replaced.

Pretty straight forward but I always like to pull the base off the old C27 capacitor (2200uF, 40V) and re-use it on my replacement capacitor.  The three-pronged base of the capacitor provides good support on the circuit board and is the negative terminal of the capacitor...so it is very handy to re-use on my replacement cap.

Here is a survey of the PCB 1 capacitors after I replaced them.  I like to replace all of the electrolytic capacitors 4.7uF and smaller with WIMA MKS, non-polarized capacitors (the red ones in the photo).

Next is the PCB 2 assembly.  It houses the microcomputer IC (a 40-pin device).  There is just one electrolytic capacitor on this board and it is for the +5 VDC power required for the uC device.  In this case, the capacitor is blown as seen in the photo below.

On the restoration for this board I remove the uC device first so I can replace the 40-pin socket with a newer one.  While the C1 capacitor is better exposed I replace it.

Now the Beogram 8002 uC device is re-installed.

REMINDER: Always take electrostatic protection precautions when handling sensitive electronic components such as digital integrated circuit devices.

Also, re-inserting a 40-pin device into a socket is not as easy as you might think.
The pins will never line up perfectly and care must be taken not to accidentally bend a pin while getting them all in place.

There is a lone control wire for the uC reset signal from PCB 2 that attaches to a terminal post on PCB 1.
The wire is a small gauge, shielded wire that often breaks where it solders onto the connector for the terminal post.  

That was the case on this Beogram 8002 so I added some extra support when I re-installed the wire.

PCB 1 and PCB 2 are now complete.  I will wait to re-attach the PCB 2 top lid until I do some Beogram 8002 functional testing. 

The electrolytic capacitor inside the Beogram 8002 transformer assembly is a non-polar capacitor that the Beogram requires for the platter motor to turn.  It is the starting phase capacitor and since it didn't fit on PCB 1, the engineers located it in the transformer compartment.

The value of the phase capacitor is different for different line frequencies.  In the US, where the line voltage is at 60 Hz, the Beogram 8002 phase capacitor is 27uF.

The Beogram 8002 Control Panel doesn't have any capacitors to replace but I do like to take it apart for cleaning, checking and installing a little test connector.

This Control Panel is in very nice condition.

The black plastic tabs in the photo that attached the PCB to the Control Panel frame are often broken (Who knows why).

These are all accounted for.

The highlighted module in the photo is where a single lamp and two LDR devices live.
The two large screws adjust the amount of light that passes from the lamp to each LDR.
This mechanism sets the idle voltage control for the Beogram 8002 servo motor that moves the tangential arm assembly.  The B&O service manual says to set the screws so the Forward and Reverse scanning functions are at an idle voltage level of 620mV.

These voltages feed into the positive input of the Op-amps controlling the tangential arm servo motor.
The 620mV level is the input level for the Forward and Reverse controls where they are not driving the motor forward or reverse.

When someone is pressing down on the Forward or Reverse scanning buttons a spring loaded aperture allows more light to the LDR and sends a higher voltage to the servo motor control to move the arm assembly forward (or backwards).

The adjustment of these scanning function screws is always a pain for me.
To set the 620mV level the LDR is measured to ground.
There are no convenient test points provided on the control panel and there have been times when I have wanted to check the LDR levels without completely opening up the Beogram.

For that reason I always install a little test connector that is accessible by pulling off the Control Panel.
That way the measurement and adjustment can be made at any time later.

Here are some photos to demonstrate....

The underneath side of the Control Panel is much cleaner than other Beogram 8002 units I have worked on. Very nice.

Here are my three test wires for measuring the two LDR devices.

...and here is the test connector installed and ready to use.

Everything is now complete where I can do a quick test to see if the Beogram 8002 comes to life.

I assembled all of the components on my bench with the floating chassis and plugged the Beogram 8002 in to AC power.

Happily I got the red dot on the display indicating "standby" and I observed the little wiggle of the platter as power is applied to the system.

The platter turn functions worked with both 33.33 and 45 RPM speeds able to lock in as expected.

I pressed Play and the Beogram arm assembly moved forward...Then it stopped moving.

That isn't totally unexpected during a "first power on" test.  It usually means there is a problem with the scanning LDR assembly in the Control Panel that I mentioned earlier.

Time to connect up my handy test connector and measure the LDRs.

Sure enough, the voltages for the scanning LDR devices were well over 1 V.  Too high over the 620mV level they should be at.  Of course this messes with the Beogram servo control circuit and the arm tends to stop.

I was able to adjust the LDR voltages to a level where the Beogram would operate but it was with the LDR voltage steady-state values of around 800mV.  However, that was with the adjustment screws fully opened up.

That isn't a good long term solution so I will have to return to the Control Panel assembly and do some work on the LDR devices. 

I want the LDR voltage levels to be around the 620mV idle voltage level with plenty of room for adjustment of the adjusting screws.

Beomaster 4400 (2419): Headphones Jack Restoration

I thought I was done with the Beomaster 4400, but I had completely forgotten about the jammed in 3.5 mm headphones adapter:

After removing it it looked like this:

While I was blissfully listening to some nice jazz on the public radio on this lovely Beomaster 4400, it occurred to me that there was something missing. Then it dawned on me that the receiver was lacking its headphones jack bezel. It must have been pushed in when the adapter hit something hard and then went missing after someone opened the Beomaster up to have a look. The headphones jack was also mashed in. Ruffians!:

After taking the jack out it looked like this:

I straightened the jack bracket as good as I could with my vise. In the meantime I obtained a spare bezel. This allowed me to finish up the repair:

With a straightened bracket the jack sits close enough to the bezel to hold it in place from the backside. From the front it looks like this:

Too bad that the banged-in adapter damaged the panel cutout a bit, but I guess for a more than 30 years old unit, this Beomaster is in pretty nice shape nonetheless.

Allright...looks I am finally done! All good in Beomaster land! I really started to like listening to this receiver, but now it is time to ship it back!

Beocord 9000: Repair of a Broken Out DIN-7 Jack With 3D Printed Inserts

It turned out that fixing the broken out DIN 7 jack of the Beocord 9000 that I just started to work on was easy. The part is exactly the same as they used for the Phono input of the Beomaster 8000. Last year I developed a 3D printed part that can resurrect these sockets when their flimsy tabs break off that normally prevent them from falling into their panel cutout. When the tabs break off due to the force applied while inserting a cable plug the jack gets pushed into the enclosure. Here is a picture of the broken jack:

These are the 3D printed tabs that replace the broken off parts:

I made a short video that shows how to install them and gives a demonstration of the repaired plug:

This shows the end result:

After the DIN jack was fixed and the tape drive was installed back into its spot, I finally gave this Beocord its first spin. I made a recording using the Beomaster 4400 that I restored recently, and I played back a nice mix tape of Donald Byrd tunes from the early 70s that I had recorded a while ago on my own 9000. Lovely!

However: One segment of the display does not work, 

and I also found a 'mystery piece' in the Beocord enclosure when I initially took out the drive:

The left part is the one that I found lying at the bottom of the enclosure. The right part is its counter part from the right side of the head carrier assembly. The broken part holds down the left side of the carrier, i.e. it is mandatory that it gets fixed. Otherwise, the heads might be in a non-spec position. I found out about this part in an excellent thread on Beoworld that was started by 'Sonavor' when he rebuilt one of his eight Beocords (kudos to owning that many! It appears, and this should please my wife, I still have a long way to go until my addiction reaches this level!!...;-).

Unfortunately, I was not able to find the 2.5mm bearing ball that goes along with the spring. The ball is needed to let the head carrier slide beneath the spring without generating too much friction. Luckily, I had the second ball for taking measurements and I was able to find small batches of these balls on Amazon Prime, so this may get fixed in a couple of days.

Beomaster 8000: Repair of a Broken Phono Jack with a 3D Printed Insert

The input jacks (sockets) of the Beomaster 8000 are weakly designed. They are made from a plastic that gets brittle over the years, and frequently the tabs that fix the jacks in the socket panel break off when a phono or tape plug is inserted. When that happens the jacks fall into the panel.

So far the remedy was to obtain a replacement from a carcass...a saddening thought. Beolover has a no-carcass policy! Parting out one should really be the very last resort!

Luckily, the 1980s designers of the jacks had a few looks too many at the cheap American cars that were made during this period (remember the Dodge Omni??), and that inspired them to also cheap down their design of these plugs.

To save plastic, they introduced recesses below the jack surface, which probably reduced the weight of the jacks by about 20%. It occurred to me that these recesses could be used to anchor a 3D printed insert, which would restore full functionality and get close to the original looks of the jacks. I made a brief video about the repair procedure (some pics are below):

The STL file of the inserts with printing instructions can be found on my website at www.beolover.com. I will also be happy to supply this part on request.

Here is a pic of the broken jack:

And with the 3D printed inserts in the recesses:

And after re-installing the jack together with the inserts:

It looks and feels pretty much like an original jack...there is a slight irregularity across the surface of the tabs due to the 3D printing raster. Oh well...it is never perfect! We can only strive!

Beomaster 8000: Wire Bridges on Microcomputer Board (#9) and Broken Phono Jack

Before I put the Beomaster 8000 back together for a test-drive in the living room together with his play-pals, the Beocord 9000 and the Beogram 8000, I cleaned and de-oxidized all the contacts on the microcomputer board (PCB #9), and had a look at the inner sanctum, the EMI shielded processor cans. Usually one needs to re-solder the few vias that are on this board, since they tend to be poorly soldered...clearly in the 80's the PCB technology was not that advanced, yet. Anyway, what I found in this particular Beomaster was remarkable. Someone already had put in the B&O recommended wire bridges (and then some...), and they were directly soldered to the processor pins. Unbelievable! Here is a pic:

While the soldering appears to have been carried out with some capability, I would never do it this way...the only parts of the Beomaster 8000 that are truly non-replaceable are the microcontrollers that contain proprietary coding, i.e. one would have to extract the code from a working one, if one would want to attempt replacing it with a NOS chip...

Anyway, clearly, this needs to be left as is. I could not risk to expose those rarefied microcontroller pins to another heat-cool cycle. In a way, since the chips survived this assault, this solution is probably the most reliable...several fewer spring based contacts in between the controllers and their slaves...so I decided to just replace the two electrolytic capacitors on this board and move on.

Here is a pic after putting in the caps:

The last thing that needs to get fixed in this Beomaster is a broken phono jack in the 'socket panel' that lost its tabs that prevent it from popping into the panel when trying to plug in the Beogram:

I am working on a creative solution, since not even Dillen of Beoworld.org has this part available.  He said it is rare, since it often breaks...Another day, another 3D print...;-)